The invention relates to a device for inserting a thread into a transport tunnel formed in the weaving shed of a pneumatic weaving machine, by means of a flowing fluid, said device comprising at least one injector with a mixing tube joined with the throat thereof.
A similar device is known. The mixing tube of the injector therein generally has a circular cross-section in order to minimize the interior circumferential surface area of the mixing tube and thereby to minimize the friction losses of the transport air flowing along said surface. Generally the thread will not leave the mixing tube along the mixing tube axis but along a path deviating from the mixing tube axis. It will be clear that said deviation is smaller when the mixing tube diameter is smaller. However, in order to permit the passage of the air quantity necessary for the thread transport the mixing tube diameter has a minimum limit. This minimum determines the dispersion of the points where the thread may leave the mixing tube in order to be received in the transport tunnel.
Now for different reasons it is desirable to keep the cross-section of the transport tunnel, which e.g. is formed from the reed lamellae, as small as possible. However, the smaller the cross-section of the transport tunnel is, the greater is the possibility that the thread leaving the mixing tube is not "catched" by the entrance cross-section of the transport tunnel so that thereby the occurrence of a weaving error is induced.
The invention aims at making provisions whereby even with relatively narrow transport tunnels, a reliable transmission of the thread from the mixing tube to the transport tunnel is guaranteed. According to the invention therewith the obtained recognization is taken into account that the distance along which the thread may maximally deviate relative to the ideal path according to the mixing tube axis in a direction perpendicular to the plane of the warp threads, constitutes the critical item.
According to the invention the mixing tube is deformed at its exit end such that the exit cross-section is narrowed in at least one direction while the total cross-sectional area at this point is at least not essentially decreased relative to the remainder of the mixing tube.
In a practical embodiment of the device according to the invention the mixing tube has been flattened at the exit end along a short distance.
Through the measure according to the invention the directional stability of the thread is increased at least in one direction namely in the direction in which the mixing tube has been narrowed.
Due to the deformation or narrowing respectively, that the friction surface presented to the transport air is increased but this increase of the friction surface is very small since the deformation or narrowing respectively is limited to the extremity of the mixing tube.
The inventive measure may also be advantageously applied if, for inserting the successive weft threads, more than one, e.g. two injectors are used, from which alternately one or more threads are inserted into the weaving shed, such as e.g. is described in the Dutch patent application No. 7903273. With the known construction according to the said patent application the assembly of injectors is pivotably arranged, namely such that each time one of the mixing tubes, at their exit ends situated mutually closely, enters an operative launching position relative to the entrance cross-section of the transport tunnel.
According to the invention the exit ends of the mixing tubes have been squeezed in a direction perpendicular to the line connecting the centers of the tube cross-sections.
By squeezing the exit cross-sections of the mixing tubes not only the directional stability of the threads supplied by each of the mixing tubes is improved but likewise the total exit cross-sectional area of the mixing tubes becomes situated within the influence of the entrance cross-section of the transport tunnel. Thereby when switching from one injector to another a substantially smaller angular rotation suffices and even a stationary arrangement of the injector assembly is possible which may lead to an important simplification.
In a particular embodiment according to the invention the mixing tube has been deformed at its exit end such that the exit cross-section is formed by a core cross-section having a plurality of extra versions extending therefrom in a radial direction. In this embodiment during operation a relatively large air velocity will be present in the core cross-section. The core cross-section thereby becomes a preferred area for the nesting of the thread. Thereby the directional stability of the thread leaving the mixing tube is improved not only in a direction perpendicular to the plane of the warp threads but also in the direction of the warp threads.
This embodiment is also particularly advantageous with injectors having a widening mixing tube such as described e.g. in commonly assigned copending U.S. application Ser. No. 394,936 for Method for Conveying a Flexible Thread by Means of a Pressurized Gas. For it is that in those cases the decrease of the directional stability caused by the widening of the mixing tube is compensated for by the effect of the deformation of the mixing tube exit end as applied according to the present invention.